1. Field of the Invention
The present invention relates to a method of cleaning a chemical vapor deposition processing chamber having deposits on an inner surface thereof. The invention also relates to a method of etching a layer on a silicon wafer. The inventive methods have particular applicability in semiconductor manufacturing.
2. Description of the Related Art
In the semiconductor manufacturing industry, extensive use is made of fluorinated gases which possess significant global-warming-potential (GWP). These compounds are commonly referred to as greenhouse gases or global-warming gases. Examples of such gases include, but are not limited to, fully fluorinated compounds, such as CF.sub.4, C.sub.2 F.sub.6, C.sub.3 F.sub.8, NF.sub.3 and SF.sub.6, and partially fluorinated compounds, such as CHF.sub.3.
As defined herein, the term global-warming compounds (GWCs) will be used to denote such compounds. These compounds typically have long atmospheric lifetimes and are efficient at absorbing infrared radiation, which contributes to the phenomena of global greenhouse effect.
The impact of a global-warming compound on climate change is measured by its global-warming-potential, which is described in D. Wuebbles, Weighing functions for ozone depletion and greenhouse gas effects on climate, Annu. Rev. Energy Environment, 1995, 20:45-70, the contents of which are herein incorporated by reference. As defined in that document and as used herein, GWP is expressed as the time-integrated radiative forcing from the instantaneous release of a kilogram (i.e., a small mass emission) of a trace gas expressed relative to that of a kilogram of the reference gas, CO.sub.2, according to the following equation: ##EQU1##
where n is the time horizon over which the calculation is considered, a.sub.x is the climate-related, radiative-forcing response due to a unit increase in atmospheric concentration of the gas in question, and [x(t)] is the time-decaying concentration of that gas and the corresponding quantities for the reference gas are in the denominator.
Many global-warming compounds are employed in the cleaning of semiconductor processing chambers. In plasma enhanced CVD (PECVD), gases are introduced into a processing chamber and a plasma is formed therefrom. Reactive species from the plasma form a film on the surface of one or more semiconductor wafers. During such processes, the film is formed not only on the wafers, but also on all exposed surfaces of the processing chamber. To clean the chamber, global-warming compounds are conventionally employed to form a plasma which removes the deposits.
Many global-warming compounds are also employed in etching processes, used to pattern dielectric and metal thin films formed on silicon wafers. In such processes, active species produced in a plasma react with exposed portions of the thin film to form a volatile product which diffuses away from the wafer surface.
When used in chamber cleaning and etching processes, the global-warming compounds generally do not react to completion. As a result, unreacted GWCs may be present in the exhaust removed from the processing tools.
It is well known and documented that GWCs are environmentally detrimental upon release into the atmosphere. In the Global Warming Symposium, Jun. 7-8, 1994, Dallas, Tex., CF.sub.4, C.sub.2 F.sub.6, NF.sub.3 and SF.sub.6 were identified as being greenhouse gases of particular concern in the semiconductor manufacturing industry.
The semiconductor manufacturing industry is currently exploring various means to reduce the emissions of such gases to minimize their environmental impact. Such attempts have included process optimization, abatement, recovery/recycle and the use of non-global-warming chemistries. While the use of new chemistries may be the most logical long term solution, it is perhaps the most difficult solution. This is because process integrity must be maintained with the use of any new chemistry. That is, the replacement chemistry should be able to perform as well as the chemistry it replaces. This is particularly important for the etching processes.
The use of iodo fluorocarbons, such as trifluoro iodomethane (CF.sub.3 I), has recently been proposed. The use of trifluoro iodomethane as an environmentally benign alternative chemistry in plasma processing is disclosed, for example, by Misra et al, Plasma etching of dielectric films using the non-global-warming gas CF.sub.3 I, Materials Letters, 34 (1998) 415-419 and by Misra et al, X-ray photoelectron spectroscopy of aluminum alloys exposed to CF.sub.3 I plasma, Materials Letters, 35 (1998) 221-226, the contents of which articles are herein incorporated by reference.
While iodo fluorocarbons may prove to be a viable alternative to the use of global-warming gases in plasma processing, process engineers are nevertheless hesitant to use iodine-containing materials. This is due, in part, to the fact that iodine is not present in the materials conventionally employed in semiconductor processing. Hence, it is desirable to develop non-iodine containing alternatives to global-warming compounds based on constituents, the effects of which on the fabricated devices are well understood and established.
German Patent Document No. 4,232,475 A1 discloses a plasma dry-etching process employing, as the etching gas, compounds including a fluorine atom and an atom selected from chlorine, bromine and iodine, chemically bound to a carbon skeleton. The inclusion of halogen atoms in the gas compound in addition to fluorine is undesirable. As described above, the effects of iodine-containing materials on the final semiconductor device formed are not fully understood. Furthermore, brominated and chlorinated compounds are known ozone depleters, thus making them detrimental to the ozone layer.
Trifluoroacetic anhydride (TFAA), commercially available from Schumacher Company, has been proposed for use in PECVD chamber cleaning processes. However, the effects of this chemistry on electrical characteristics of the devices being formed is not fully understood. The development of other non-global-warming chemistries useful for chamber cleaning as well as for thin film etching is, therefore, desirable.
Furthermore, one drawback to the use of TFAA in chamber cleaning is its being a liquid at standard temperature and pressure. As a result, TFAA requires a special chemical delivery system for introduction into the processing chamber. Since CVD systems are typically designed to handle gas-phase chemistries, the use of a liquid-phase chemistry would require a vaporizer structure, in addition to a different type of mass flow controller (MFC) and other monitoring devices from those conventionally used. Further, liquid droplets may be entrained in the vaporized material, thereby leading to processing abnormalities. While the present invention also contemplates liquid chemistries, the development of a gas-phase chemistry is desirable for hardware simplification purposes.
To meet the requirements of the semiconductor manufacturing industry and to overcome the disadvantages of the related art, it is an object of the present invention to provide a novel method for cleaning a chemical vapor deposition processing chamber having deposits on an inner surface thereof.
It is also an object of the present invention to provide a method of etching a layer, for example, a dielectric or a metal layer, on a silicon wafer.
As a result of the invention, the release of global-warming compounds into the atmosphere and the environmental damage associated therewith can be avoided or conspicuously ameliorated.
Other objects and advantages of the present invention will become apparent to one of ordinary skill in the art upon review of the specification, drawings and claims appended hereto.